linux-kernel - Re: [PATCH v2] rcu/kvfree: Make drain_page_cache() call return directly if cache is disabled

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Date:   Mon, 24 Apr 2023 10:35:53 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     Zqiang <qiang1.zhang@...el.com>, frederic@...nel.org,
        joel@...lfernandes.org, qiang.zhang1211@...il.com,
        rcu@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: [PATCH v2] rcu/kvfree: Make drain_page_cache() call return
 directly if cache is disabled

On Thu, Apr 20, 2023 at 01:06:27PM +0200, Uladzislau Rezki wrote:
> On Tue, Apr 18, 2023 at 08:27:02PM +0800, Zqiang wrote:
> > If the rcu_min_cached_objs is set to zero at boot params, the
> > krcp->page_cache_work will not be triggered to fill page cache,
> > and the put_cached_bnode() also does not fill page cache, this
> > also means the krcp->bkvcache is always empty, so not need to
> > acquire unnecessary krcp->lock to get page from krcp->bkvcache,
> > this commit therefore make drain_page_cache() return directly if
> > the rcu_min_cached_objs is zero.
> > 
> > Signed-off-by: Zqiang <qiang1.zhang@...el.com>
> > ---
> >  kernel/rcu/tree.c | 3 +++
> >  1 file changed, 3 insertions(+)
> > 
> > diff --git a/kernel/rcu/tree.c b/kernel/rcu/tree.c
> > index 93faf9f5c58f..00620a2117de 100644
> > --- a/kernel/rcu/tree.c
> > +++ b/kernel/rcu/tree.c
> > @@ -2924,6 +2924,9 @@ drain_page_cache(struct kfree_rcu_cpu *krcp)
> >  	struct llist_node *page_list, *pos, *n;
> >  	int freed = 0;
> >  
> > +	if (!rcu_min_cached_objs)
> > +		return 0;
> > +
> >  	raw_spin_lock_irqsave(&krcp->lock, flags);
> >  	page_list = llist_del_all(&krcp->bkvcache);
> >  	WRITE_ONCE(krcp->nr_bkv_objs, 0);
> > -- 
> > 2.32.0
> > 
> Reviewed-by: Uladzislau Rezki (Sony) <urezki@...il.com>

Queued for further testing and review, thank you both!

						Thanx, Paul